Journal Article

How Spatial Resolutions Impact the Large‐Scale River Hydrodynamic Model Simulations: Analysis Focuses on Model Physics

Zhou, Xudong, Revel, Menaka, Yamazaki, Dai, Hirabayashi, Yukiko, Modi, Prakat

2025

Overview

Large‐scale hydrodynamic models are vital for flood risk assessment and understanding the global water cycle; however, their results can include uncertainties related to spatial resolution. Few studies have evaluated hydrodynamic models across a range of spatial resolutions, with most focusing on a few variables (e.g., discharge) and often neglecting performance at ungauged sites or the role of parameter optimization. We addressed these limitations by comparing Catchment‐based Macro‐scale Floodplain (CaMa‐Flood) model simulations in the Amazon River basin at different spatial resolutions, using the higher resolution as a benchmark in each comparison. We found good inter‐resolution performance in simulating discharge and water depth, with coefficients of determination exceeding 0.88 in >80% of locations. The normalized Nash–Sutcliffe efficiencies for discharge and water depth were greater than 0.83 and 0.68, respectively, in more than 75% of locations, suggesting that most locations had consistent hydrodynamics. We detected large discrepancies in discharge between simulations at ∼2.5% of locations due to limited representation of bifurcation flow, floodplain conveyance, and backwater at river confluences in the model. Water depth also differed significantly at ∼3% of locations, mainly at headwaters, due to width bottleneck sections. Flood extent patterns differed minimally between simulations around the main stream and large sub‐streams, whereas improvements in the downscaling method are required for small sub‐streams. Our results demonstrate the need to improve the representation of bifurcation channels and floodplain parameterization for specific locations, although the general river hydrodynamics patterns were well‐captured by computationally efficient moderate‐resolution (i.e., 6 arcmin) CaMa‐Flood simulations. Plain Language Summary Large‐scale models that predict how water moves are crucial for assessing flood risks and understanding the global water cycle. However, these models can have uncertainties related to their spatial resolution. Few studies have evaluated these models at different levels of detail but usually focused on a few variables or ignored areas without data and parameter adjustments. To address these gaps, we compared the Catchment‐based Macro‐scale Floodplain (CaMa‐Flood) model's simulations of the Amazon River at different resolutions, using the highest level of detail as a reference. The model simulated flow and depth at lower resolutions, achieving a strong agreement with higher resolutions at 80%–90% of locations. Most locations showed consistent results for flow and depth. Still, there were significant differences in a small percentage of areas due to the model's limited ability to represent complex flow patterns and certain channel features such as bifurcation flow, backwater effect, floodplain conveyance, and bottleneck channels, across various resolutions. Flood extent patterns were generally similar between simulations, but improvements are needed for smaller streams. Our findings highlight the need to enhance the model's representation by improving baseline river network data, although overall, the model's moderate‐resolution simulations effectively captured general river hydrodynamics. Key Points Sub‐grid parameterization makes moderate‐resolution (6 arcmin) simulation results almost similar to those at higher resolution Causes of differences in simulated hydrodynamics in a few locations are attributed to the characteristics of river models' physics Better sub‐grid topography treatment (bifurcation, river confluence, channel width) would potentially enhance low‐resolution simulations

• Publisher: John Wiley & Sons, Inc,American Geophysical Union (AGU)
• Subject: Amazon River / Backwaters / Creeks & streams / Environmental risk / Flood risk / flood risk assessment / Floodplains / Floods / Fluid mechanics / Headwaters / Hydrodynamic models / Hydrodynamics / Hydrologic cycle / Hydrological cycle / large‐scale models / Parameter estimation / Parameterization / Physics / Risk assessment / River basins / river hydrodynamics / River networks / Rivers / Simulation / spatial resolution / Stream flow / Topography / Variables / Water depth / Water levels